We plan to purify to homogeneity an opsonin (n-opsonin) from sera and characterize it biochemically. We will study its specificity in regard to colloid particles, its mechanism of action, and its turnover rate in animals under various conditions. We want to establish its site of synthesis and the production of such an opsonin by various species. We want to determine the relationship of N-opsonin to other opsonic systems.